1. Field of the Invention
The invention relates to a contact element intended for a superconducting cable unit, for medium or high voltage.
2. Description of the Related Art
A superconducting cable may comprise, around a longitudinal axis and inside a thermal jacket containing a refrigerant, a supporting central core which may be tubular and also contain a refrigerant and on which are concentrically arranged superconducting layers of phase No. 1 to phase No. N in the case of a multiphase-phase cable, usually three phase, and finally a screen layer of a neutral conductor. A dielectric layer is arranged between each superconducting layer.
At the end of a superconducting cable, the current and the voltage have to be transmitted from a part at cryogenic temperature to a part at ambient temperature. This transition has to be designed in such a way as not to transmit a significant quantity of heat by thermal conduction and not to generate significant losses by Joule's effect in the passage of the electrical current. It must also not cause electrical flashover between the parts connected to the earth or to another phase. It is therefore necessary to simultaneously manage the thermal gradient, the effects of the current and the electrical field.
Conventionally, an electrical bushing of a certain length, of the order of a meter or even more, possibly provided with a specific device for controlling the electrical field, is mounted at this end of the cable.
The patent document DE 10 2004 034 494 describes a contact element provided with an electrical connection element with a bushing ensuring the management of the electrical field. Because of its length, this bushing also ensures the management of the thermal gradient between the temperature of the refrigerant, in which the contact element is located, and the ambient temperature at the free end of the bushing.